Ethanol production from grains, primarily corn, has grown rapidly from the late 1990's through today with much of that growth occurring between 2004 and 2009 now culminating in a national production of over 16 billion gallons per year in 2016. The U.S. Renewable Fuels Standard (RFS2) calls for production of 15 billion gallons per year in conventional biofuels (grain based ethanol) starting in 2015 forward. It also specifies increasing amounts from cellulosic sources from current levels to over 15 billion gallons per year by 2022. This will be a very difficult achievement unless advanced technologies for biomass conversion are teamed up with innovative means to recover fuel ethanol and other bio-fuels. These innovations must make the best use of the conversion streams for added value products as well as process these streams with limited energy input.
Internationally, there are similar goals to increase alternative biomass conversion to fuels and such aggressive growth plans will require government support and private equity investment. Both will only be possible if the supported technologies are economically viable and sustainable.
World supplies and availability of crude oil are not limitless although recent years have revealed still new accessible pools of fossil fuels. Developing economies often have limited local natural resources and underdeveloped distribution channels for energy products. These factors create considerable incentive for the development and use of alternative fuels as well as production of the same in remote locations making use of regionally available biomass, particularly that which must be landfilled or burned openly. Furthermore, environmental concerns have required use of additives which aid in oxygenation of the motor fuels. These additives have created concerns of their own for environmental damage. Ethanol has established wide popularity as a fuel additive capable of addressing these concerns, particularly when mixed with gasoline to form a mixture known as gasohol. Gasohol may contain up to about 10 vol. % ethanol and could be permitted in amounts up to 15 vol. %, without modifications to presently designed automobile engines being required, thereby extending the volume of motor fuel availability by a like percentage.
The current major source of the ethanol used in gasohol is derived primarily from the fermentation of mash, usually from corn or wheat or other grain. Natural fermentation is able to produce an ethanol-water product mixture containing, at most, about 12 wt % to 15.5 wt % ethanol. This mixture may easily be concentrated by distillation to about 91% to 95% ethanol. Higher concentrations of ethanol, however, as required in gasohol are obtained only by expenditures of great amounts of energy and great difficulty due to the formation of an ethanol-water azeotrope at about the 95% ethanol concentration. A means of achieving greater than 95% ethanol concentration without 1) such a great expenditure of energy or 2) loss of the used energy is thus extremely valuable. Such schemes have been employed in the past to recover heat from azeotropic distillation employing tertiary entrainers such as benzene (U.S. Pat. Nos. 4,372,822, 4,422,903 and 5,035,776). Others earlier had considered the option of using heat from the stripping/rectifying column to heat an azeotropic distillation (U.S. Pat. Nos. 1,860,554 and 4,217,178). Additionally, one invention considered generating steam from the heat in overhead vapors of the azeotropic distillation (U.S. Pat. No. 4,161,429) and another used mechanical vapor recompression of the overhead vapors to recover heat in the fashion of a heat pump for heating the azeotropic distillation column(s) (U.S. Pat. No. 5,294,304). Since about 1998 the prevalent approach to producing ˜99.5 wt % ethanol from the 91 to 95% distillation overheads is the use of pressure vacuum swing adsorption (PVSA) on a 3A Zeolite media. Several effective methods of implementing this process have been proposed and employed. One of these is U.S. Pat. No. 9,308,489 B2, “Adsorption Process for the Dehydration of Alcohol”.
Further discussion regarding advances in grain based ethanol production and integration of the distillation, evaporation, and dehydration units of operation can be found on U.S. Pat. No. 7,867,365 B2 “Ethanol Distillation with Distillers Soluble Solids Recovery Apparatus.
The recovery of bio-fuels, chemicals, and volatiles such as ethanol and methanol from developing biomass conversion processes and cellulosic conversion processes is made more challenging since many of these processes result in an aqueous stream of dilute bio-fuel and or chemicals. Many of these processes require large quantities of water and the resulting sugar solution for fermentation is dilute resulting in low ethanol, methanol, or other bio-fuel/chemical concentration. Conversion of cellulose and hemicellulose in biomass results in a mixture of six carbon and five carbon sugars which limits the final ethanol concentration that yeast can produce. For some biomass conversions a gaseous mix may be produced and directly metabolized by yeast, algae, or other organisms to produce chemicals, ethanol, methanol, butanol, or many other compounds specific to the organism's metabolic pathways. These gaseous mixes can be a synthesis gas, exhaust flue gas rich in carbon dioxide, carbon dioxide from traditional dry mill fuel ethanol production, or any number of other sources emitting carbon dioxide.
Recovering these chemicals including ethanol from dilute solutions can be prohibitively energy intensive. Some processes for recovery require low temperature operation to maintain the viability of the microorganism producing the chemical weak feed stream. Some can operate at higher temperatures where the biologicals have been removed by other means. For all, the very high concentration of water requires innovative approaches to limit energy consumption and maximize the recovery of valuable chemicals and fuels. This invention is intended to solve this energy problem.